WO 01/32735 relates to a process for making a foam using a prepolymer having an NCO value below 20% by weight. Such a process has as disadvantages that an extra production step is needed to make the prepolymer and that such prepolymers have often a higher viscosity, which may hamper the easiness to make the foams. Still further, the hardness of the foams is not high enough for foams having a relatively low hard-block content and a relatively high density.
WO 01/60884 relates to a process for preparing a flexible polyurethane foam using a high amount of a polyol having a high oxyethylene content and a high primary hydroxyl content together with a polyol with a medium oxyethylene content (see e.g. example 8). When the experiment was repeated in a closed mould no satisfactory foam was obtained.
WO 01/32736 relates to a process for preparing foams using similar polyols together with a polyol having a low oxyethylene content. The process is a one shot process or a prepolymer process wherein the prepolymer has a high NCO value. The foams obtained have visco-elastic properties.
U.S. Pat. Nos. 5,594,097 and 4,559,366 relate to the use of polyols having an intermediate amount of oxyethylene groups (i.e. from 20-50% by weight) in preparing flexible foams. U.S. Pat. No. 5,459,170 relates to prepolymers from such polyols.